1. Technical Field
The invention relates generally to the production of glass fiber, and more particularly to glass forming tubes used in the production of glass fiber.
2. Description of Related Art
In the production of glass fiber for various intended applications, glass strands are manufactured from molten glass streams flowing through orifices formed in a die or bushing. The strands are drawn in the form of continuous filaments and the filaments are gathered into base strands, which typically are then wound into rolls or “cakes”.
Before they are gathered together in the form of strands, the filaments are coated with a coating of a binder or sizing composition. The binder or sizing serves as a lubricant and protects the strands during the fiber production process. The binder or sizing can also facilitate the binding of the filaments to one another within the strands. Good integrity is particularly important in textile applications where the strands are subjected to strong mechanical stresses. The binder or sizing also can facilitate an improved bond between the glass strands and the matrix material in a fiber-matrix composite material.
The binder or sizing compositions (hereinafter referred to generally as “coating compositions”) typically are water-based. The water generally represents 90% by weight of the composition, and hence the water must be evaporated after application of the composition. Therefore, some type of drying device must be used to heat the coated glass strands. Typically, the coated glass strands or fibers are wound about forming tubes to form rolls or cakes, and then the cakes are heated in an oven or the like so as to dry/cure the coating.
Most forming tubes are formed of paperboard that is coated with silicone or the like to render the tubes impervious to the liquid coating composition, since the tubes are exposed to the composition when the wet coated fibers are wound onto the tubes. The coating also renders the tubes impervious to vapors. During the curing/drying process, vapors are generated by evaporation of the volatile component(s) of the coating composition. It has been found that vapor pressure that builds up in the cake can rise to such a level that the forming tube can implode. Additionally, the curing/drying process can take a considerable amount of time (e.g., up to 48 hours or more), and hence a significant amount of energy is expended.